SC-3 Calibration Values

Discussion in 'Guiding and Adaptive Optics - StarChaser and AO' started by Russell Croman, Sep 25, 2020.

  1. Russell Croman

    Russell Croman Cyanogen Customer

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    Good morning,

    I received a new SC-3 and installed it on the scope. It is very insensitive to light compared to another SC-3, and I can't get anything other than a big blob from a very bright star, even though focus was set to match the other unit (same optical system).

    Looking in DLConfig, I see the calibration values below. The eGain looks nonsensical for sure. Not sure about what the other values are supposed to be.

    This unit came with FW version 3, but it wouldn't talk to MaxIm 6.23/DLAPI 1.8.5.0. I upgraded to FW 4, and it now connects fine and goes through the motions of taking exposures, but with poor results.

    Please advise.

    Thanks,

    Russ


    Screen Shot 2020-09-24 at 10.44.30 PM.png
     
    Russell Croman, Sep 25, 2020
    #1
  2. Doug

    Doug Staff Member

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    The focus problem is not related to the gain setting, as that is an optical/mechanical issue.

    Check that the mirror position is the same - it affects the focus too.

    I'll ask @Tim to weigh in on the gain issue. Assuming this is s/n SC1300M-20030901 the eGain was measured correctly at 4.8 e-/ADU. It looks to me like it wasn't written to the camera's EEPROM. He may be able to log in remotely and program it.

    The gain/offset adjustments are not used in the StarChaser. The factory defaults for the CMOS sensor always work.
     
    Doug, Sep 25, 2020
    #2
  3. Russell Croman

    Russell Croman Cyanogen Customer

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    That was just a starting point for the focus... we tried to dial it in, but were only successful in getting a slightly smaller big blob.

    Happy to fire up TeamViewer for some remote programming if that's needed.

    Here's the serial number info:

    Screen Shot 2020-09-25 at 9.00.31 AM.png

    -Russ
     
    Russell Croman, Sep 25, 2020
    #3
  4. Doug

    Doug Staff Member

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    Okay I guess that record was for your other unit. That serial number has an eGain of 4.6 e-/ADU.
     
    Doug, Sep 25, 2020
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  5. Tim

    Tim Staff Member

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    PM sent
     
    Tim, Sep 25, 2020
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  6. Russell Croman

    Russell Croman Cyanogen Customer

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    Update... the gain value was actually correct. The DLConfig utility reports the gain value to six significant figures (4.61683), but formats the value such that the most significant digit and decimal point are cut off when the UI window is at its default size. So I was only seeing the fractional part of the gain value (61683).

    So now I'm back to scratching my head about why I can't get any reasonable star images. The pick-off mirror and focus are very close to the SC-3 that this SC-3 replaced. The shutter is working properly. I can shine a light down the OTA and see the entire guide sensor, so the guide sensor can see the sky. I'm flummoxed.

    -Russ
     
    Russell Croman, Sep 25, 2020
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  7. Doug

    Doug Staff Member

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    I'm going to suggest that the formatting of that display box be changed slightly to avoid a repeat of the confusion.

    As for the insensitive to light part... those units are all fully tested at the factory and this unit was working well. Also since it is a CMOS sensor it is unlikely for the sensor to fail in this fashion - if it failed we simply wouldn't get any image from it.

    Can you post a light frame and a dark frame from the sensor (FITS format)?
     
    Doug, Sep 25, 2020
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  8. Russell Croman

    Russell Croman Cyanogen Customer

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    I've attached bias, dark, and light frames. The lights are just what I can get during the day with the scope pointed toward some varying field in the observatory with the roof closed. I also included 2x2 binned versions... I was using 2x2 binning trying to focus on stars... it didn't occur to me to try 1x1 binning. Including them in case there is some interesting difference between 1x1 and 2x2.

    -Russ
     

    Attached Files:

    Russell Croman, Sep 25, 2020
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  9. Doug

    Doug Staff Member

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    There does appear to be a mild gradient on the light frame, after dark subtraction.
     
    Doug, Sep 25, 2020
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  10. Russell Croman

    Russell Croman Cyanogen Customer

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    I tried to pick a spot in the observatory to point the scope that had some light variation, so that's intentional and expected.

    -Russ
     
    Russell Croman, Sep 25, 2020
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  11. Doug

    Doug Staff Member

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    Okay then, those images look normal.

    My usual suggestion at this point is to point the telescope at the moon. It's hard to miss! That will verify that everything is working and you can very easily get the focus in the correct ballpark.
     
    Doug, Sep 25, 2020
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  12. Russell Croman

    Russell Croman Cyanogen Customer

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    Will do... thanks.

    -Russ
     
    Russell Croman, Sep 25, 2020
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  13. Russell Croman

    Russell Croman Cyanogen Customer

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    Mystery solved: the pick-off mirror had a clear protective film on it. The guider is seeing stars just fine now. Sensitivity seems completely normal.

    -Russ
     
    Russell Croman, Sep 25, 2020
    #13
  14. Doug

    Doug Staff Member

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    LOL, that's caught people out a few times now. The film is a good idea but if it's forgotten it does mess things up! I'll see about adding a QA inspection step for that, so we remove it just before the unit is sealed in plastic.
     
    Doug, Sep 25, 2020
    #14

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